Calcium receptor-active compounds are known in the art. One example of a calcium receptor-active compound is cinacalcet HCl, which is described, for example, in U.S. Pat. No. 6,001,884, and has the following structure:

Such calcium receptor-active compounds may be insoluble or sparingly soluble in water, particularly in their non-ionized state. For example, cinacalcet has a solubility in water of less than about 1 μg/mL at neutral pH. The solubility of cinacalcet can reach about 1.6 mg/mL when the pH ranges from about 3 to about 5. However, when the pH is about 1, the solubility decreases to about 0.1 mg/mL. Such limited solubility can reduce the number of formulation and delivery options available for these calcium receptor-active compounds. Limited water solubility can also result in low bioavailability of the compounds.